An error occurred while attaching module (Dynamicweb.Frontend.Content)

System.Data.SqlClient.SqlException (0x80131904): Login failed for user 'Dynamicweb_DanskRideForbund'. Reason: Server is in single user mode. Only one administrator can connect at this time.
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()
   at Dynamicweb.Data.DatabaseConnectionProvider.CreateConnection(Boolean open)
   at Dynamicweb.Data.Database.CreateConnection()
   at DanskRideForbund.BusinessLayer.Provider.DataProvider.GetCollection[T](SqlCommand command, SqlConnection connection) in D:\a\1\s\DanskRideForbund.BusinessLayer\Provider\DataProvider.cs:line 41
   at DanskRideForbund.DataAccessLayer.HorseData.GetHorsesById(ICollection`1 horseIds) in D:\a\1\s\DanskRideForbund.DataAccessLayer\HorseData.cs:line 120
   at DanskRideForbund.BusinessLayer.Provider.HorseProvider.GetHorseById(String horseId, Boolean includeVfL, Boolean isExternal) in D:\a\1\s\DanskRideForbund.BusinessLayer\Provider\HorseProvider.cs:line 223
   at DanskRideForbund.CustomModules.HorseModule.HorseModuleFrontend.ShowHorse(HorseHelper helper, DataArea dataArea) in D:\a\1\s\Application\CustomModules\HorseModule\HorseModuleFrontend.cs:line 149
   at DanskRideForbund.CustomModules.HorseModule.HorseModuleFrontend.GetContent() in D:\a\1\s\Application\CustomModules\HorseModule\HorseModuleFrontend.cs:line 45
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)
ClientConnectionId:555993f3-bb9c-427a-b041-51f2f1a2b913
Error Number:18461,State:1,Class:14